I have seen many examples and photos of plastic surgery failure on TV. That sounds horrific. I am single and double, and I often look big and small. I've considered cutting double eyelids before, but if it fails, it's better to be natural. Look online and show it to your sister. Maybe she will say that there are so many failures in cutting double eyelids. . . But you have to let her know that if she is unlucky, plastic surgery is tantamount to disfigurement and it will be really painful.